System of electrical distribution.



J.-L. WOODBRIDGE. SYSTEM OF ELECTRICAL DISTRIBUTION.

APPLICATION IILI D MAR. 20, 1908.

Patented Feb. 14, 1911.

INVENTOR. W Wot A4615 b WITNESSES Jr/M A TTORNE Y.

UNITED STATES PATENT OFFICE.

JOSEPH LESTER WOODBRIDGE, or

PHILADELPHIA, PENNSYLVANIA.

SYSTEM OF ELECTRICAL DISTRIBUTION.

Specification of Letters Patent.

Patented Feb. 14, 1911.

To all whom it may concern:

Be it known that I, J osnrrr L. Woom names, a citizen of the United States, and a resident of Philadelphia, in the county of Philadelphia and State of Pennsylvania, have invented a certain new and useful System of Electrical Distribution, of'which the following is a specification.

My invention relates to systems of electrical distribution in which synchronous rotating apparatus is connected to an alternating current circuit.

The object of my invention is to provide means for suppressing or reducing the effects of harmonics in the Wave of alternating electro-motive-force developed by the synchronous apparatus.

It is particularly applicable to apparatus in which, to produce certain results, the field distribution is such as would tend to produce abnormal distortion of the wave shape from the true sine curve, as might occur under some circun'istances in rotary converters designed as described in Letters Patent Nos. 679,812 and 679,813, issued to me under date of August 6th, 1901, and in Letters Patent No. 873,714, issued toJ. L. Burnham, under date of December 17th, 1907.

The general nature and scope of my invention will be more clearly understood by reference to the following description in connection with the accompanying drawings, in which- I Figure 1, is a diagrannnatic representation, illustrating the distribution of magnetic field around the armature of a synchronous machine, to which reference will be made in explaining the principles uponwhich my invention rests, while Fig. 2,

shows the armature of a synchronous machine connected to an alternating current circuit in accordance with my invention.

In Fig. 1, the'line A B represents the de veloped periphery of the armature of a synehronous bi-polar machine. The broken lines C D E F and G H I J represent the distribution of field flux around the. armature, the ordinate f at any point represent ing the flux density at that point. The point A which is fixed with reference tothe field is taken as the origin and the angular distance from A to any other point around the periphery is represented by 0.

We Will consider the elect-ro-motive-force The electro-motive-force developed in any elementary portion d6 of the armature Winding at any instant will be proportional to the field strength and the magnitude of (10, and may therefore be represented by the expression Kfd0, in which K, is a constant depending on the design of the machine, the speed, and the units employed. The total electro-motive-force 11 developed in the section X Y, at any instant corresponding to the angular distance will then be Substituting in thisthe value of f, in equation (1) and integrating, we have Y which may be reduced to g i sin. 3(r/ sin. sin. 5(g0- a etc} It Will be seen that this expression, which represents the wave shape of the alternating electro-inotive-foree developed between the points X and Y, consists ol a fundamental sine wave,

1 2l\a, sin. l, sin. g -a (the variable being the angle. 4;).upon which is superposed various harm nies ol the twin 2162x111. 1f .4". al o',,)

in which n, may be any odd integer. The higher harmonics in the series become negligible, both on account of the ,increasing value of a in the denominator ofthecoellicient and also on account of the well known increase in the damping effect of any inductance in the circuit, at higher frequencies. It is, however, desirable to suppress as far as possible the lower harmonics in any synchronous apparatus connected to an alternating current system. It is known that the third harmonic and its multiples may be suppressed in athree phase circuit by Y- .:onnecting the primaries of the static trans- ."ormers which are employed between said synchronous apparatus and the circuit, lly examining the expression 2K2? sin. sin. n(-o',,) it will be seen that this may be reduced to zero by selecting a suitable value for [3, that is, a value such that sin.

ihis will result if we make or any integral multiple of 71'. Thus if it is desired to suppress the 5th harmonic, we may make from which [3 .1. ()r it it is desired to suppress the 7th harmonic, we may lllnlte from which [2 .8mm ()r, it [3 be given an intern'iediate value, l'or eXalnple .Silvr, both the 5th and the 7th harmonies will be reduced to small values as compared with their maximum values. The maximum values of all the harnumics in the series will occur when 3 :17. corresponding to the diametrical connection of the armature For if for all odd integral values of a. 1f

corresponding to the usual three phase delta l connection, the third hari'nonic and its mill- 5 t iples will disappear, since sin. =0, 4L1

but all of the other harmonics will bear the same proportion to the fundamental as they do with diametrical connection when [3 :11. Fol-1f for all odd inte i'al values of n exee it mulb tiples of 5.

it, however, [3 .8%, 'we have 7 7 the th harmonic will be rclativel y small regardless of the ,value of [3, and 5 should be determined with reference to the 7th harmonic, its value being more nearly .857. It on the other hand,

Y 7 is relatively small, [3 should be determim-d with reference to the bth harmonic, and its value should be more nearly .S-ir. 'lhe. relative values of a, aml a, will depend upon the distribution ol. the tield tlux, and may be determined when the locus of the lines l) l6 l and (i ll 1 J, in Fig. l, is known.

In Fig. 2, are shown means for combining the two methods of suppressing, harmonies above referred to. that is, the Y connection of the primaries ol the static transtormers designed to eliminate the third harmonic and its multiples in combination with suitable location ol the alternating current taps to the armature winding, designed to reduce to a minimum the 5th or the 7th harmonic or both. in this diagram, Q, is the armature of the bi-polar synchronous machine, N and S being, resptwtivelythe north and south poles of the magnetic circuit. 1, 2, and 3, are the conductors of a three phase circuit to which are connected respectively the primary windings 4, 5, and

6, of three static transformers, "the well known Y connection. bein shown. The secondary windings 7 8, an 9., -f these transformers are connected to the armature Q,

in such a way that each includes. an armature section whose angular span ,8 is. made suitable to reduce to a minimum the th and 7th harmonics as explained above. The angular displacement between the three armature sections is 120 permitting these sections to be connected by means of the static transformers to the three phase circuit. The angle [3 as here'shown has an intermediate value between .81 and .8571. It may, however, be made to approach or equal either of these limits according to whether it is desird to produce the greatest reduction in the 5th or 7th harmonicsf It will be understood that modifications may be made in the details without departing from'the spirit of my invention, hence I do not limit the invention further than the prior state of the art may require, but

Having thus described the nature and objects of my invention, what I-claim as new and desire to secure by Letters Patent 1s- In combination, a three phase alternating current circuit, a synchronous dynamo electricv'machine having an armature and a winding uniformly'distributed over its periphery, three pairs oftaps from said armature winding, each pair including a span not less than 144; and not more than 154.3 electrical degrees, said spans successively displaced l'electrical degrees around the periphery, static transformers having three independent secondarywindings each connected to one of said pairs of taps and three primary windings Y-connected to the circuit.

In testimony whereof I have hereunto signed my name.

JOSEPH LESTER WOODBRIDGE. Vitnesses:

K. M. GILLIGAN, FRANK E. FRENCH. 

